In web fed rotary printing presses, which are e.g. used for printing commercials or for printing newspapers, it is often desired to change one or more printing plates mounted to the plate cylinders of the press, without interrupting the printing operation. An exchange of the printing plates may for instance be desirable, if during a running newspaper production, the latest news have to be actualized and printed on the front page of the current editions or if different editions of the same newspaper are distributed in different areas under different names, so that the title of the newspaper has to be changed during the production run.
U.S. Pat. No. 5,063,844 describes a lithographic rotary printing press having a blanket-to-blanket printing unit, in which two plate cylinders can be alternatingly engaged and disengaged with one of the blanket cylinders, in order to carry out a flying plate exchange, while the printing press is in operation. During the flying plate exchange, both blanket cylinders of the printing unit are driven and are in rolling contact with the running paper web, while the plate cylinder which has been disengaged from the blanket cylinder is disconnected from the common drive motor, decelerated to a stop and re-accelerated after the printing plates have been changed.
German Patent DE 44 05 658 C2 describes a printing unit of a lithographic web fed rotary printing press for carrying out an on the run exchange of printing plates. The printing unit comprises two blanket cylinders and associated plate cylinders respectively, which are alternately engaged and disengaged with an impression cylinder over which the running web is passed. Each of the blanket cylinders is driven by its own separate motor and drives the associated plate cylinder via a gear train. The impression cylinder is driven by a further separate motor.
GB 2 309 668 discloses a blanket-to-blanket printing unit for carrying out a flying plate exchange in which the plate cylinders remain in rolling contact with the running web, while the blanket cylinders of the unit are alternately engaged and disengaged with their associated blanket cylinder. The blanket cylinders are constantly coupled to each other via meshing pinion gears and are driven by the main drive motor of the press via a line shaft. The blanket cylinders, however, are coupled to the pinion gears of the blanket cylinders via clutches and associated further pinion gears respectively. For exchanging the printing plates of one of the plate cylinders, while the press is in operation, the drive connection to the plate cylinder is interrupted by activating the respective clutch and the plate cylinder is decelerated by an auxiliary motor. After exchanging the printing plates, the auxiliary motor re-accelerates the plate cylinder up to press speed, before it is reengaged with its associated blanket cylinder. Hence, at least two auxiliary motors are required for performing a flying plate exchange. The document further describes the arrangement of two flying imprinter printing units on top of each other, wherein the engagement and disengagement of the plate cylinders and blanket cylinders is performed crosswise, in order to provide for a continuous printing operation.